1. Field of the Invention
The present invention relates to a group of compounds classified in the field of organic chemistry as aldehyde or ketone O-[(3-indolyl)(aryl or heteroaryl)methyl]oximes which are useful as color formers in pressure-sensitive carbonless duplicating systems and thermal marking systems; to processes for the preparation thereof and to pressure-sensitive carbonless duplicating systems and thermal marking systems containing the same.
2. Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as color formers for carbonless duplicating systems. Among the most widely recognized classes are the phenothiazines, for example, benzoyl leuco methylene blue; fluorans, for example, 2'-anilino'6'-diethylaminofluoran; phthalides, for example, crystal violet lactone; methine dyes, for example, Michler's hydrol and derivatives thereof and various other types of color formers currently employed in commercially accepted carbonless duplicating systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457 and 3,041,289, which issued July 5, 1955, July 23, 1957 and June 26, 1962, respectively. Many of the color formers in the prior art suffer one or more disadvantages such as low tinctorial strength, poor light stability, poor xerographic copiability, low resistance to sublimation limation and low solubility in common organic solvents, the latter disadvantage thus requiring the use of specialized and expensive solvents in order to obtain microencapsulated solutions of sufficient concentration for use in pressure-sensitive copying systems.
The most pertinent prior art relative to the present invention appears to be U.S. Pat. No. 4,124,227 issued Nov. 7, 1978 which discloses oxime ethers of Michler's hydrol as color precursors in pressure-sensitive copying systems.